Manual and automatic control servo-system



Dec. 11, 1962 H. H. KoPPEL 3,068,387

MANUAL AND AUTOMATIC CONTROL SERVO-SYSTEM Original Filed Sept. 21, 19595 Sheets-Sheet 1 ATTORNEY Dec. 11, 1962 H H, KOPPEL 3,068,387

MANUAL AND AUTOMATIC CONTROL SERVO-SYSTEM Original Filed Sept. 2l, 19595 Sheets-Sheet 2 FIG. 2

INV ENTOR. HAROLD H. KOPPEI.

il. XM@

AnmNEY Dec. 11, 1962 H. H. KoPPEl. 3,068,387

MANUAL ANO AUTOMATIC CONTROL sERvO-sTsTEM Original Filed sept. 21, 1959INVENTOR. HAROLD H. KOPPEL ATTORNEY Dec. 11, 1962 H. H. KOPPEL 3,068,387

MANUAL AND AUTOMATIC CONTROL SERVO-SYSTEM Original Filed Sept. 21, 19595 Sheets-Sheet 4 POSITION EF/loa x1 i E Lll if) N 0 o mi N ,9 INVENTOR.E- HAROLD H. KOPPEL g BY a www 9 ATTORNEY DeC- 11, 1952 H. H. KoPPELMANUAL ANO AUTOMATIC CONTROL sERvO-sYsTEM Original Filed sept. 21, 19595 Sheets-Sheet 5 INVENTOR.

HAROLD H. KOPPEL ,Il QQ S6@ X Ew United States Patent Gtice 3,068,387Patented Dec. 11, 1962 3,068,387 hilANUAL AND AU'JFMATIC CONTROLSERVG-SYSTEM Harold H. Koepel, South Euclid, Dhio, assigner to BaileyMeter Company, a corporation of Delaware Continuation of. appiicationSer. No. S4L171, Sept. 21,

1959. This appliication June 5, 1961, Ser. No. 116,238 19 Claims. (Cl.S18- 28) This invention relates to control apparatus and moreparticularly to apparatus for transferring control of a variable fromone method of control to another.

The alternate use of two or more methods of control in a control systemis well known to those skilled in the art. For example, a provision foralternate use of two different servo mechanisms is often desired so thatin the event of failure of one mechanism a reserve mechanism will beavailable to maintain the control system in operation. Another exampleof the alternate use of two different methods of control is in a controlsystem where provision is made for both automatic control and manualcontrol. At times it is desired to operate the control system manuallyand a transfer from automatic to manual control is made through theprovision of a suitable transfer or selector station.

One major problem in the transfer of control from one mechanism toanother is the fact that inequality of the outputs of the automaticcontroller and manual controller at the instant of transfer will producea shock or bump which may result in instability or damage to the system.In the past this condition has been avoided through manual adjustment ofthe manual controller output or system setpoint to equalize the twocontroller outputs prior to transfer. Such a manual adjustment, how--ever, is objectionable due to the fact that it is time-consuming and insome cases diiiicult to accomplish such as in a control system havingreset action.

It is a principal object of this invention to effect an automatictransfer of the control of a variable from one mechanism to another andvice versa without manual adjustment of the output of either mechanismprior to transfer.

Another object of the invention is to automatically equalize the outputsof two controllers prior to transfer of control from one controller tothe other or vice versa.

Another object of the invention is to provide an improved automatictransfer selector station for transferring control of a variable fromone mechanism to another.

Other objects and advantages will become apparent I from the followingdescription taken in connection with the accompanying7 drawings wherein:

FIG. 1 is a schematic illustration of the application of the inventionto a control system;

FIGS. 2, 3, 4 and 5 are views similar to FIG. l illustrating otherembodiments of the invention; and

FIG. 6 is a block diagram of the system illustrated in FIG. 5.

FIG. l Embodz'ment Referring more particularly to FIG. l of thedrawings, there is shown a single element control system comprising afinal control element or valve 10 which is actuated pneumatically inaccordance with the iiow rate in a conduit 12 to control the flow rateof fluid in a conduit 14. A transmitting device 16 is responsive to thei'iow rate of fluid in conduit 12 as is represented by the diferentialpressure across a primary measuring element 13, and is effective toactuate the movable core 20 of a movable core transformer having aprimary winding 2.2 and a pair of serially connected, oppositely woundsecondary windings 24 and 26. The primary winding 22 is connected acrossa suitable source of alternating voltage as indicated schematicallywhile the secondary windings 24 and 26 are coupled to a demodulator 2S.With this arrangement a modulated signal is supplied to the input of thedemodulator 28 with a carrier frequency corresponding to the frequencyof the A.C. source, the modulated amplitude of the signal beingproportional to the ilow rate of the fluid in conduit 12. Circuitry ofthis nature is well known to those skilled in the art, and therefore,further description is deemed unnecessary.

The demodulator 28 is effective to remove the A.C. carrier signal toestablish a variable D.C. signal at its output terminals proportional tothe flow rate in conduit 12. The transmitting device 16 and demodulator28 may be calibrated to produce any desired range and level of directvoltage at the output terminals of demodulator 2S in the range of liowrates encountered. However, as disclosed in Hornfeck et al. applicationSerial No. 805,019, this direct voltage signal may be caused to vary inthe range of `25 to +25 volts.

The output of demodulator 28 is compared with the output of a manuallyadjustable circuit 30 at a summing junction indicated schematically at32 to establish an error signal representative of the variation of theflow rate from set point. The output of the circuit 30 is manuallyadjustable in the range of -25 to +25 volts to provide a set pointvoltage with which the output of demodulator 2S is comparedalgebraically.

The error signal thus established at the summing junction 32 isimpressed on the input terminals of an automatic controller 34 which maybe composed of one or more plug-in control action units of the typedisclosed in Hornfeck et al. application Serial No. 805,019. Thecontroller 34 illustrated in FG. 1 comprises a single plug-in controlaction unit having proportional action for producing an output signal atterminal 36 proportional to the error signal applied to the inputterminals 38.

in general the controller 34 comprises a high gain, low output impedanceD.C. amplifier 40` having a passive input resistor R1 and a passivefeedback resistor R2. As described in the aforementioned copendingapplication Serial No. 805,019, the gain of the controller 34 isdetermined by the relative sizes of resistors R1 and R2.

As will later be described in more detail, during automatic operation ofthe system the output of the controller 34 is applied directly to anelectric to pneumatic converter 44 which is effective to establish aproportional pneumatic signal for application to the valve 10. Suchconverting evices are well known to those skilled in the art, and adetailed disclosure and description of this component is deemedunnecessary.

During manual operation of the system, however, the controller 34 isdisconnected from the converter' 44 and an electrical signal isestablished manually and applied to the converter 44. As a result thevalve 10 is positioned independently of the controller 34 output andindependently of variations in the flow rate in conduit 12..

A manual-automatic selector station 4S is provided for transferringcontrol of the valve 10 from the controller 34 to a manually operativecontroller which includes a potentiometer circuit 52 energized by asuitable source of direct voltage and having a movable contact arm 54the potential of which depends on its position relative to a slidewire56. The potentiometer circuit 52 is completed by a second resistor 5Shaving a grounded center tap connected to an input terminal of theconverter 44. With this arrangement the voltage of contact arm 54 willbe the manual control voltage.

The movable Contact arm 5d is adapted to be connected by switch meanslater to be described to the other input terminal of the converter 44and is positioned by an electric motor i acting through linkage 62. Themotor t a; the manual control voltage 5t) is provided with the usualenergizing windings 64. and which are connected in an electric circuitwith a capacitor 6- across a suitable source of alternating voltage.Energization of the windings 64 and 66 is controlled during manualoperation by pair of manually operative pushbutton switches itl and 72.Switch 7@ is effective when closed depending upon the condition of otherparts later to be described to connect the energizing wind ing 66directly across the A.C. source and to connect the energizing windingLiftin series with the capacitor 63 across the same source. As a resulta 90 phase relationship will be established between the two windingscausing the motor 6ft to rotate in one direction. lf switch lil is openand switch '72 closed this phase relationship will be reversed causingrotation of the motor in the opposite direction. Thus, closure of theappropriate switch TIS or 72 will effect manual positioning of the valvelil in the desired direction.

As previously mentioned it is necessary that the outputs of twoalternate control mechanisms be equal at the instant of transfer ofcontrol to avoid introducing a shock or bump into the system. With thepresent invention this is accomplished automatically as will now bedescribed.

Referring rst to a transfer' from automatic operation to manualoperation, means are provided for effecting continuous positioning ofthe contact arm 54 in accordance with the output of controller 3d duringautomatic operation so that any instant during automatic operation thepotential of contact arm will equal the output potential of controller3d and a transfer may be safely made. This means comprises a servoamplifier 7o, which may take various forms well known to those skilledin the art, effective to control energization of a pair of relays A andB having normally open contacts A1 and B1 respectively. The contacts A1and B1 are connected in shunt circuits with the switches 7G and .72respectively, and thus energization of the relays A and B will effectrotation of the motor 6d and positioning of the contact arm 54 inopposite directions.

The motor 6l) is also effective to position a contact arm 7S relative toa slidewire resistance gil connected across a voltage source (not shown)forming part of armplier 76 to establish a voltage feedback signal inservo amplifier 76 equal to the potential at contact arm 78 and themanual control voltage at contact arm Sd. age is continuously comparedwith the output potential of controller in the servo amplier 7&3 duringautomatic operation. The relays A. and B are energized in accordancewith the polarity of the voltage difference to effect rotation of themotor i@ in a direction to maintain the two voltages `rental. Thus,through selective energization of the relays and B continuous follow-uppositioning of the contac nl 5.. will occur to maintain equal to theoutput of t e controller 3d during automatic operation.

During manual operation of the system, positioning of the contact armfrom servo amplifier 76 is discontinued and the energizing circuit forwindings 64 and 66 is conditioned to transfer control of the motor allto ranually operative switches 7d and 73. The operator by opening andclosing the switches 7u and 72, may then exercise manual control overthe position of the valve ld as hereinbefore described.

Since during manual operation the contact arm 54 is positionedindependently ot the controller 3d output separate means includingy acapacitor C is provided for equalizing the two voltages at the instantof transfer back to automatic operation. An understanding of theoperation of this means will be facilitated by the accompanyingmathematical analysis of the various circuit conditions the instant oftransfer.

The output e0 of the controller 34 during both automatic or manualoperation may be expressed as follows:

wherein em is the error or input signal applied to the con This voltn.

spesse? troller l is the o l as determined by the relai-.ve magnitudesR1 and At the instant of transfer it is desirable that the followingrelationship be established:

e controller 34 of the resistors eczem where em is the manual controlvoltage on contact arm 54 and manually determined by the operatorthrough actuation of switches lil and '72.

To accomplish this condition the capacitor C is connected by switchmeans later to be described between the Contact arm 5ft and the outputterminal 36 of the controller 3.4.-. With this arrangement the voltagecc of the capacitor C may be expressed mathematically as follows:

As the transfer is made the switch means is effective to simultaneouslyconnect one side of the capacitor C to the input terminal of theamplifier ttl through an input resistor Rc equal in size to the resistorR2 and the other side of the capacitor to ground at 86. At this instantthe controller 34 output e0 will be equal to:

Through substitution in Equation 4 for ec the following equationresults:

Thus, at the instant of transfer the controller output e0 will equal themanual control voltage am resulting in a smooth bumplcss transfer backto automatic operation. From this instant on the capacitor C willdischarge through the resistor Re until the charge on the capacitor C iszero.

Since the resistors and E2 are equal in size the term ec in equation f-lappears at the output of the controller 3d without a gain factor K.rl`hus, when the capacitor C has discharged completely the resistor rcand capacitor C will be completely ineffective in the circuit and normalautomatic operation will exist wherein the controller output en will beagain equal to Kem. lt will be apparent to those skilled in the art thatthe discharge time of the capacitor C may be varied through propersizing of this element.

in effect the addition of the capacitor C and resistor Re to theproportional control action unit .lv produces a summing control actionunit of the type disclosed in copending application Serial No. 805,619,this summing unit existing only at the instant of transfer' from manualto automatic operation to eftect equalization of the controller outputvoltage and the manual control voltage as described above.

Referring now to the switching means for initiating and effecting thehereinbefore described operations, relay coil D is connected in serieswith a pair of pushbutton switches and 9d across the A C, energizingsource for the system. rihe switch l 'rte as Hand is biased to normallyclosed position and adapted to be actuated to an open position by theoperator to effect a transfer' from automatic to manual operation. Theswitch 931 indicated by Auto is biased to a normally open position andis adapted to be actuated to a closed position by the operator toinitiate a transfer from manual to automatic operation.

The relay coil D is provided with a plurality of contacts D1, D2, Dg,B4, D5, and De which are biased to their open positions assumed duringdeenergization of the relay coil D. Similarly, tue relay D is providedwith a plurality of contacts D7, B3, E9, D19 and DH which are 'biased toclosed positions assumed during dcenergization of the relay lt isbelieved that the function and operation of the pushhutton switches ilnfl 9" and relay D and will become apparent from the following summarythe operation of the system illustrated in FIG. l.

Assume that at startup the operator momentarily actuates the switch 90to a closed position to effect automatic operati-on of the system.Closure of switch 9@ will complete an energizing circuit for relay coilD to effect opening of contacts D7, D8, D9, D10 and D11 and closure ofcontacts D1, D2, D3, D4, D5 and D5. `Contacts D3 are connected in ashunt holding circuit around the switch 9i? and will maintainenergization of the relay D when the switch 90 is subsequently releasedto its yopen position by the operator. The system is now conditioned forautomatic operation.

As a result of energization of relay D the output voltage e9 of thecontroller 34 is applied directly to the converter 44 through contactsD1; while application of the manual control voltage em to the converteris prevented by open contacts D7. The output e9 of the controller 34,however, is applied by conductor 92 directly to the servo amplifier 76to effect follow-up positioning of the contact arm 54. Contacts D4 andD5 connected in series with contacts A1 and B1 respectively close topermit energization of windings 66 and 64 in response to closure ofcontacts A1 and B1 respectively -as a result of operation of the servoamplifier 76. Contacts D8 and D9 connected in series with the switches7! and 72 respectively are open during automatic operation to preventenergization of the motor windings as a result of accidental actuationof the switches 70 and 72.

During automatic operation contacts D17 D2 are closed and contacts D10,D11 `are opened to prevent charging of the capacitor C and to render thesame ineffective in the controller 34 circuit. As a result of thecircuit conditions thus established, the valve 10 will be continuouslypositioned from the output of controller 34; which is proportional tothe flow rate in conduit 12. In addition, the servo amplifier 76 isresponsive to the output signal of the controller 34 to continuouslyeffect follow-up movement of the contact arm 54 to maintain thepotential of contact arm 54 equal to the controller 34 output Voltage.Thus, at any instant during automatic operation the manual controlvoltage at contact arm 54` is equal to the output of controller 34.

Assume now that the operator desires to operate the valve l@ manually.To accomplish this the manual switch Si; is momentarily actuated to anopen position to break the energizing circuit for the relay D,dcenergizing the same. As a result contacts D5 will open disconnectingthe controller 34 output from the converter 44 and contacts D7 willclose to connect the contact arm 54 and apply the manual control voltageto the converter' 44. Contacts D4 and D5 will open and the contacts D5and D9 will close to transfer control of energization of the win-dingsof motor 6@ to the switches 'Tit and 72 which may be selectivelyactuated by the operator to effect positioning of the valve lt).

ln addition, contacts D1 and D2 open upon deenergization of relay D andcontacts D19, D11 close to connect the capacitor C between the outputterminal 36 of the controller 34 and the contact arm 543. As a result acharge is developed across the capacitor C equal to the algebraic sum ofthe output voltage e9 of the controller 34 and the manual controlvoltage e111 as illustrated by Equation 3.

When it is desired to return the system to automatic operation theoperator momentarily closes switch 9G to effect reenergization of relayD and reestablishment of the holding,y circuit through contacts D3.Contacts D5 will close and contacts D7 will open to apply the controller34 output to converter 44, while contacts D5, D5, D5, D9 will beactuated to transfer control of energization of the motor 60 to contactsA1 and B1.

-Conacts D19, D11 will open while contacts D1 and D2 will close toconnect the capacitor C in series with the resistor Rc between theamplifier input terminal and ground at 86. Thus, at the instant yoftransfer the output voltage e0 of controller 34 is expressed byEquations 5 and 6 and sucses? ,6 l n equal to the manual control voltageem. As u result a burnpless transfer from manual back to automaticoperation is achieved. In a Very short period of time the capacitor Cwill discharge completely and become ineffective in the system duringthe automatic positioning of valve l0.

FIG. 2 Embodment Referring now to FIG. 2 of the drawings there is showna control system having a proportional control action unit generallysimilar to that shown in FIG. l but utilizing an electric motor actuatedvalve positioning system in place of the pneumatic system illustrated inFi'G. l. Parts similar in function to those shown in FiG. l have beengiven like reference numerals.

in general the operation of the embodiment of PEG. 2 is similar to thatof FIG. l with th-e exception that in transferring from automatic tomanual operation the drive is merely deenergized and then reenergizedmanually as desired to effect positioning of the valve iti. Therefore,the problem of equalizing two controller outputs does not exist intransferring from automatic to manual opeizciionA Referring now to thespecic structure disclosed in 2, the valve 10 in this case is positioneddirectly by electric motor 10i) through a linkage 162. The motor ltt'iis provided with energizing windings 64 and 66 similar to the motor 6)in FIG. l. A position feedback transmitter tl4 is also actuated by themotor ltt) and serves to establish a direct voltage signal at its outputterminals proportional to the position of valve liti. The outputterminal 36 of the controller 34 is adapted to be connected by contactsD5 during automatic operation to one side of an input winding (notshown) of a magnetic amplitier M6. The output of the position feedbacktransmitter 164 is applied to the other side of this input Windingduring automatic operation by contacts D15 to establish input to theamplifier 106 proportional to the voltage dilerence. Relay coils E and Fare adapted to be alternately energized by the amplifier 1.96 duringautomatic operation according to the polarity of the voltage error ordifference signal applied to the magnetic amplier Accordingly, theamplifier 166 will effect rotation of the motor tl during automaticoperation to maintain the output voltage of transmitter fitti equal tothe output voltage of controller 34a Thus, the positioning systemcomprises a closed loop voltage balance servo system. For a morecomplete description of the structure and operation of such a voltagebalance positioning system reference is made to copending applicationSerial No. 786,820 filed on January 14, 1959, by Anthony J. Hornfeck etal., now Patent No. 3,015,768.

in the system of FIG. 2 the output of position feedback transmitter M4is equivalent to the output of potentiometer circuit 52 of FIG. l, itbeing necessary to also equalize the outputs or" transmitters fue andcontroller 34 prior to a transfer from manual to automatic operation.Thus, the contacts D11 are effective during manual operation to connectthe output of transmitter 104 to one side of capacitor C.

A pair of normally open contacts D12 land D14 of relay D are connectedin series with the relay coils E and F respectively to preventenergization of the relay coils E and F by the magnetic amplifier 166during manual operation. Manually operative switches 70 and '72 are inthis case connected in series with contacts D11 and D9 to controlenergization of the coils E and F and effect manual positioning of valvelll. Contacts D9 and D9 are open during automatic operation to renderswitches 76 and 72 inoperative in the system.

rl`he operation of the system illustrated in FIG. 2 is generally similarto the operation of the system illustrated in FIG. l. To effectautomatic operation of the system at startup the switch 96 ismomentarily closed by the cperator to effect energization of relay coilD which remains energized through its holding contacts D5. Contacts D5and D15 close to apply the outputs of controller 34 and transmitter i494to the magnetic amplifier illu, and switch D11 opens to prevent chargingof the capacitor C by the output of transmitter ldd. Contacts D12 andD14 will close while contacts DE, and D2 will open to cause the magneticamplifier 3% to control energization of Windings E and E and positioningof valve hf). With these circuit conditions E11 will equal Kem as statedin Equation l.

When it is desired to operate or position the valve 'rtl manually theoperator opens switch 3S to break the holding circuit through contactsD3 and effect deenergizaticn of relay D. As a result contacts D6 and D15will open disconnecting the controller 3ft and transmitter 104 from theamplifier lilo. Contacts D12 and D14 will open and the motor will bedeenergized. Closure of contacts D2 and D9 will enable the operator toeffect manual positioning of the valve l@ through actuation of switches7d and 72.

The contacts D1, D2, D10 and D11 are effective during manual operationto connect the capacitor C between the output terminal 36 of controller34 and output of transmitter llild. Thus, similar to the embodiment ofFIG. l the charge ec 'on the capacitor C may be expressed by Equation 3.ln this case, however, Eln will be the output voltage of transmitteritll which will be equal to the controller output voltage at the instantof transfer. Thus, when the switch 99 is subsequently actuated by theoperator to transfer back to automatic operation, a smooth, bumplessinstantaneous transfer will be achieved similar to the embodimentillustrated in FIG. l.

FIG. 3 Embodiment Referring to PEG. 3 of the drawings there is shown anautomatic transfer selector station similar to that disclosed in FIG. lbut adapted for use with a controller llltl having re et action inaddition to proportional action. As disclosed in more detail incopending application Serial No. 305,()l9 such a controller comprisesinput and feedback resistors R1 and R2 and in addition a capacitor C2which is connected in series with the resistor R2 in the feedbackcircuit to provide the reset or integrating action.

With the controller of FIG. 3 the reset capacitor C2 is employed toequalize the output of the controller llt) with the manual controlvoltage at the instant of transfer from manual to automatic operation inthe same manner as: capacitor C of FlG. l. Thus, the capacitor C2 servestwo functions, that of providing reset action and that of effectingequalization of the controller Mtl output voltage at the instant oftransfer.

The relay coil D in this case is provided with contacts D111 which closeduring automatic operation to complete the feedback circuit throughresistor R2 and capacitor C2. As in the case of the FIG. l embodimentthe output terminal 36 is connected during automatic operation bycontacts D6 to the converter 44. Also, the controller llt) output isapplied through conductor 92 during automatic operation to the servoamplifier i6 to effect continuous followup movement of the contact arm:'54 as described in connection with FiG. l.

The system is transferred to manual operation similar to the embodimentillustrated in FlG. l. In this case, however, deenergization of relaycoil D at the instant of transfer is effective to close contacts D11 toconnect the right hand side of the capacitor C2 to the contact arm 54.ln addition, contacts D17 close simultaneously to connect the resistorR2 directly to the output terminal 36 causing the controller 11@ tobecome a proportional controller. With this circuit arrangement if thegain of the controller lli is K the output e0 will be equal to Kem.Thus, during manual operation the output voltage of the controller litiwill continuously equal the input voltage and the reset action will beremoved from the controller.

It will be apparent that during manual operation the controller 1l@output e0 will equal Kem if the gain of the controller is K. lnaddition, the manual control vol*- Sill Hifi) 8 age em will be suppliedto one side of the capacitor C2 while the controller output voltage e0will e applied to the other side thereof. Thus, the charge ec2 acrossthe capacitor C2 during manual operation may be expressed by thefollowing equation:

When a transfer back to automatic operation is subsc- -quently made asdescribed in connection with FIG. l, the contacts D17 open and contactsD111 will close to reconnect the capacitor C2 in series with theresistor R2 to establish reset operation of the controller 11d. At theinsant of actuation of contacts D11 and D16 the output voltage e0 willbe equal to Kem plus the voltage or charge egg across the capacitor C2as expressed by the following equation:

Through substitution of the value of @c2 as given by Equation S, thefollowing equations result:

and

Thus, from the above it will be apparent that the controller il@ outputvoltage e0 at the instant of transfer from manual to automatic operationis equal to the manual control voltage em. This condition is establishedby capacitor C2 and its associated circuitry.

After a transfer from manual to automatic operation is made thecapacitor C2 will slowly cause the controller 11th to integrate untilnormal automatic control action is obtained. Thus, after a shortinterval of time normal reset operation of the controller 110 willoccur.

It will now be apparent that the embodiment disclosed .in FiG. 3operates in a manner similar to that disclosed in FIG. l. Duringautomatic operation continuous follow-up positioning of the contact arm54 is accomplished so that at the instant of transfer from automatic tomanual Voperation the output of controller 110 will equal the voltage ofcontact arm 54 or the manual control voltage. As a result a buinplesstransfer from automatic to manual operation may be made at any instantby the operator merely by actuating switch as previously described.During i 1anual operation the controller 110 is converted from a resetcontroller to a proportional controller and the capacitor C2 is utilizedto equalize the controller 110 output with the manual control voltage atthe instant of transfer back to automatic operation.

The use of the capacitor C2 as a means of equalizing the manualcontroller and automatic controller output voltages in the embodiment ofFIG. 3 has a decided advantage in that only a very limited number ofadditional parts are required over those normally employed in a controlsystem having a reset controller.

FIG. 4 Embodiment FIG. 4 of the drawings illustrates the application ofthe reset controller Mtl and transfer means illustrated in FlG. 3 to theelectric positioning system illustrated in FIG. 2. in this embodimentthe contacts DG are employed to connect the controller liti to themagnetic amplifier lilo while the contacts D18 are utilized to ccnnectone side of the reset capacitor to the output terminal of the positionfeedback transmitter ltlli.

The operation of the embodiment of FIG. 4 is generally similar to thatdisclosed in FIG. 3 except that the voltage applied to the capacitor C2by contacts D18 during manual operation is generated by the positionfeedback transmitter Mld which as discussed in connection with 'F.G. 2is generally equivalent to the potentiometer circuit Sti in function.Thus, similar to the FIG. 3 embodiment the reset capacitor C2 serves twofunctions that of providing reset action during automatic operation andestablishing equalization of the manual and automatic control voltagesprior to a Itransfer of manual to automatic operation. As described inconnection with FlG. 2 the motor is merely deenergized upon a transferfrom automatic to manual operation and, therefore, an equalization ofthese two voltages is not necessary when transferring in that direction.

FIG. 5 Embodz'ment The applications of the invention disclosed in FIGS.1-4 of the drawings utilize single element control systems. In FIG. 5 ofthe drawings there is shown an application of the invention to aZ-element control system wherein the position of a final control elementis controlled in accordance with the variations in two differentvariables. In FIG, 6 there is shown a block diagram of such a controlsystem. More particularly, a steam pressure transmitter 150 establishesan electric signal which is compared with a set point signal at 32 toestablish an error signal representative of the departure of a steampressure condition from set point. This signal is provided with resetcharacteristics in a controller or control action unit 134 of the typeshown in FIGS. 3 and 4 and disclosed in 4detail in copending applicationSerial No. 805,019.

The output signal of the control action unit of controller 13d iscompared with a signal representative of the steam flow established by atransmitter 136 in a summing control action unit 13S which may also beof the type disclosed in copending application Serial No. $315,019. Theoutput of control action unit 138 is taken through a selector station1461 which as now will be described is also provided with means foreffecting bumpless transfer between manual and automatic operation.

Referring now to FlG. 5, the controller 134 is of the proportional plusreset type illustrated in FIGS. 3 and 4 comprising an amplifier dit,resistors R1 and R2, and reset capacitor C2. The control action unit orcontroller 133 as described in copending application Serial No. 895,019comp-rises an amplifier 40 having a pair of input resistors R3 and R4, afeedback resistor R5 and input terminals 3S which are adapted to beconnected respectively as shown to the outputs of controller 134 andtransmitter 136. The controller 134 is effective to produce a voltagedrop across resistor R4 equal to its output voltage and the transmitter1.36 is similarly effective to produce a voltage drop across resistorR3. With this arrangement the output of controller 133 at its terminal36 will be proportional to the sum of the outputs of controller andtransmitter 136, the relative effectiveness of the two signals beingdependent on the relative values of the resistors R3 and R1 ofcontroller 13S.

lt will be app-arent that with the 2-element control system at theinstant of transfer from automatic to manual operation or vice Versa theoutput of the summing contr-ol action unit 13S must equal the manualcontrol voltage. To accomplish this the contacts D18 are eective toapply the voltage of contact arm 54 or output of valve positiontransmitter 1M, depending on whether an electric or pneumaticallyactuated valve is utilized, to the left side of the capacitor C2.Contacts D20 serve to connect the output terminal of controller 138 tothe right side of the capacitor C2 during manual operation. The contactsD16 and D11 serve to transform the controller 134 into a proportionalcontroller duringI manual operation as described in connection withFIGS. 3 and 4.

in operation of the embodiment illustrated in FlG. 5, when the system ison automatic operation continuous follow/up movement of the contact arm54 will occur when the positioning system disclosed in FIGS. 1 and 3 isutilized. Thus, the manual control voltage will equal the output ofcontroller 13S. When a positioning system or the type disclosed in FlGS.2 and 4 is utilized transfer 1) is accomplished by deenergizing themotor 101), and the problem of bumpless transfer to manual operationdoes not exist.

When la transfer from automatic to manual operation lis made, the unit134 is converted from a reset unit to a proportional unit by contactsD16 and D17. Contacts D18 apply the manual control voltage em to oneside of the capacitor C2 and contacts D20 apply the output voltage ofcontroller 138 to the other side of the capacitor C2. Thus, .the voltagece2 across the capacitor C2 may be expressed as follows where e4 is theoutput voltage of controller 138:

The output voltage e4 may be expressed by the following equation Where,e3 is the output voltage of transmitter 136, e2 is the output voltage ofcontroller 134, and R1, R2, R3, R4 and R5 are the values of theresistance elements.

:El Fiel-E he lost equation may be combined with Equation 12 to producethe following expression for c62:

Upon transfer from manual to automatic equation the conta-cts D16 andD17 are effective yto connect the capacitor C2 into the feed backcircuit of unit 134. Thus, lthe output voltage e2 of unit 134 at thisinstant may be expressed as follows:

Equation 16 may be substituted in Equation 17 to produce the followingequation:

Substituting the -last equation in Equation 13 for e2 the followingresults:

lf R5 is made ecual to R4 the last equation reduces to Thus, at theinstant of transfer the output voltage e4 will equal the manual controlvoltage land a transfer may be safely made.

While several embodiments have been herein shown and described, it willbe apparent to those skilled in the art that many changes may be made inthe construction and arrangement of the parts without departing from thescope of the invention as defined in the appended claims.

This application is a continuation of my application, Serial No.841,171, tiled Sept. 21, 1959.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In a contro-l system, the combination comprising, a iinal controlelement, first electrically operative means for controlling the positionof said control element, second electrically operative means forcontrolling the position of said control element, an electric relayhaving contact means effective in one position of said relay to connectsaid first electrically operative means to said control element yand inanother position of said relay to connect said second electricallyoperative means to said control element, circuit means including `anelectric capacitor associated with said rst and second electricallyoperative means, means including said relay for charging said capacitorin proportion to the voltage difference of the outputs of said first andsecond electrically operative means during control of said con-trolelement from one of said electrically operative means and for connectingsaid capacitor so charged to equalize the outputs of Said first andsecond electrically operative means at the instant of transfer ofcontrol from said one of said electrically operative means to lthe otherof said electrically operative means.

2. In ra control system, the combination comprising, a final controlelement, means responsive to variations in the magnitude of a variablefor establishing a first electrical signal having a predetermined rangeand representative of the magnitude of the variable, lan electriccontroller for amplifying said signal and having a feedback circuit, anelectric capacitor connected in said feedback circuit for introducingreset characteristics into said first signal, separate means formanually establishing a second electrical signal variable in said range,relay means operative when energized to effect control of said controlelement from said controller and when deenergized to effect control ofsaid control element from said manual means, and first contact meansassociated with relay means effective to apply Ithe output signals ofsaid controller and -said manu-al means to opposite sides of saidcapacitor respectively in the deenergized condition of said relay meansto thereby equalize said output signals at the instant of subsequentenergization of said relay means.

3. In a control system as claimed in claim 2 wherein said manuallyoperative means comprises a potentiometer circuit having a movablecontact arm for varying said second signal.

4. ln a control system as claimed in claim 3 further including a servoamplifier responsive to the difference between said first iand secondsignals, an electric motor connected to the output of said amplifier forpositioning said contact arm to maintain said Signals equal, and secondcontact means associated with said relay means effective to render saidmotor operative in response to said amplifier output in the energizedcondition of said relay means and inoperative in the deenergizedcondition of said relay means.

5. In a control system as claimed in claim 4 wherein manually operativeswitch means are provided for effecting energization of said motor insaid deenergized condition of said relay means to effect manualpositioning of said contact arm and said control element.

6. In a control system, the combination comprising, a control element,means responsive to variations in a variable for establishing anelectrical signal in a predetermined range representative of themagnitude of the variable, an electric controller for amplifying saidsignal and having an electric amplifier provided with a feedbackcircuit, an electric capacitor connected in said feedback circuit forintroducing reset characteristics into said signal, circuit meansincluding `a device responsive to the output of said controller foroperating said control element, relay means associated with said circuitmeans and having one position for rendering said operating deviceoperative in response lto said controller output signal and a secondposition for rendering said operating device inoperative in response tosaid controller output signal, manually operative switch means operativein said second position of said relay means for energizing saidoperating device to effect manual operation of said control element, andcontact means associated with said relay means for disconaser nectingsaid reset capacitor from said feedback circuit in said second positionof said relay means.

7. In a control system as claimed in claim 6 further including atransmitting device for establishing an electrical signal representativeof the position of said control element and further including secondContact means for connecting the outputs of said transmitting device andsaid controller to opposite sides of said capacitor respectively in saidsecond position of said relay means.

8. ln a control system, the combination comprising a .l control clement,first means responsive to the magnitude of a first variable forestablishing a rst electrical signal, second means responsive to themagnitude of a second variable for establishing a second electricalsignal, a first electric controller for amplifying said first signal,said controller comprising an amplifier having an external feedbackcircuit, a capacitor connected in said feedback circuit for introducingreset characteristics into the output signal of said first controller, asecond controller for producing an output signal proportional to thealgebraic sum of said first controller output signal and said secondsignal, manually operative means for controlling the position of saidcontrol element, relay means having a first position for applying theoutput of said second controller to said control element and a secondposition for effecting control of said control element from saidmanually operative means, first contact means associated with said relaymeans having one position for connecting said capacitor in said feedbackcircuit to produce said reset action and a second position fordisconnecting said capacitor from said feedback circuit, a transmittingdevice for establishing an electrical signal representative of theposition of said control element in said second position of said relaymeans, and second contact means associated with said relay meanseffective to connect the outputs of said second controller and saidtransmitting device to opposite sides of said capacitor in said secondposition of said first contact means.

9. In a control system, the combination comprising regulating means of acondition responsive to a first or a second electric control signal, afirst controller for producing the first control signal comprising anoperational amplifier, a first input impedance connected to the input ofsaid amplifier, a feedback circuit for said amplifier comprising aresistance connected between the input and output thereof for causingthe first control signal to be proportional to a first input signalapplied to said first input impedance, a second controller forestablishing the second control signal, switch means having a firstposition for connecting the output of said first controller to saidregulating means to effect adjustment thereof in accordance with changesin the first control signal and a second position for connecting saidsecond controller to said regulating means to effect adjustment thereofin accordance with changes in the second control signal, a capacitor, asecond input impedance connected to the input of said amplifiercomprising a resistance equal in value to said feedback resistance, acircuit established by said switch means in said second position whichconnects one side of said capacitor to the output of said firstcontroller and the other side of the output of said second controller,and a circuit established by said switch means in said first positionwhich connects said one side of said capacitor to said second inputimpedance and said other side of said capacitor to ground to therebyapply a second input signal to said amplifier at the instant of transferfrom said second to said first controller to cause said first controlsignal momentarily to equal said second control signal at the instant oftransfer and thereafter to gradually adjust C il 70 to proportionalitywith said first input signal as said capacitor discharges and saidsecond input signal attenuates to zero.

l0. In a control system, the combination comprising, regulating means ofa condition responsive to an electric control signal, a controllerproducing said control signal 13 comprising an operational amplifier, afirst input impedance connected to the input of said amplifier, afeedback circuit for said amplifier comprising a resistance connectedbetween the input and output thereof for causing said control signal tobe proportional to a first signal applied to said first input impedance,switch means having a first position for connecting the output of saidcontroller to said regulating means and a second position disconnectingsaid controller from said regulating means, a capacitor, a second inputimpedance connected to the input of said amplifier comprising aresistance equal in value to said feedback resistance, means producing asignal corresponding .to the status of said regulating means, a circuitestablished by said switch means in said second position thereof whichconnects vone side of said capacitor to the output of said controllerand the other side to said status signal, and a circuit established bysaid switch means in said first position thereof for connecting said oneside of said capacitor to said second input impedance and said otherside of said capacitor to ground to thereby H apply a second inputsignal to said amplifier at the instant of connection of said controllerto said regulating means to thereby cause said control signalmomentarily to equal said status signal at the instant of connection andthereafter to gradually adjust to proportionality with said first inputsignal as said capacitor discharges and said second input signalattenuates to zero.

1l. In a control system, the combination comprising regulating means ofa condition responsiveto a first'or a second electric control signal, afirst controller for producing said first control signal comprising anoperational amplifier, an input impedance connected to the input of saidamplifier, a feedback circuit for said amplier comprising a capacitorconnected between the input and output thereof for causing the firstcontrol signal to vary as the time integral of an electric input signalapplied to said input impedance, a second controller for establishingsaid second control signal, switch means having a first positionestablishing said feedback circuit connections of said capacitor and forconnecting the output of said first controller to said regulating meansto effect adjustment thereof in accordance with said first controlsignal, and a second position for connecting said second controller tosaid regulating means to effect adjustment thereof in accordance withsaid second control signal, said switch means being operative in saidsecond position to effect connection of the side of said capacitorconnected to the output of said amplifier in said first position to theoutput of said second controller and the other side of said capacitor tothe output of said amplifier so t'nat upon return of said switch meansto said first position said first control signal momentarily equals saidsecond control signal at the instant of transfer and thereaftergradually adjust to proportionality with the time integral of said inputsignal.

12. In a control system as claimed in claim 18 wherein said firstcontroller comprises a proportional plus integral operational amplifierhaving a feedback resistance connected in series with said capacitor toestablish a first control signal at the output of said amplifier havingproportional plus integral characteristics, said switch means beingeffective to disconnect said capacitor from said feedback circuit insaid second position thereby causing the output of said amplifier tovary linearly in proportion to changes in the input signal only.

13. In a control system, the combination comprising, regulating means ofa condition responsive to a first or a second control signal, meansresponsive to variations in the magnitude of a Variable for establishinga signal proportional to the magnitude of the variable, an electriccontroller for amplifying said signal to produce said first controlsignal, means for establishing said second control signal, electricallyoperative adjusting means for said last named means, switch means havinga rst position for applying said first control signal to control saidregulating means and a second position for applying said second controlsignal to control said regulating means, an electric capacitor, acircuit established by said switch means in said second position thereofeffective to charge said capacitor in proportion to the differencebetween said first and second control signals, a circuit established bysaid switch means in said first position thereof effective to connectsaid capacitor so charged in the circuit of said rst controller toequalize the first and second control signals at the instant ofactuation of said switch means from said said second to said firstposition to permit a shockless transfer of control from said secondcontrol signal to said first control signal, and means responsive tosaid first control signal in said first position of said switch meansfor actuating said electrically operative adjusting means tocontinuously equalize said second control signal with said first controlsignal to permit a shockless transfer of control from said first controlsignal to said second control signal upon actuation of said switch meansfrom said first position to said second position.

14. in a control system, the combination comprising, a final controlelement, electrically operative positioning means for said controlelement, manually operative switch means for controlling energization ofsaid positioning means to permit manual operation of said controlelement means for establishing a voltage signal representative of thecontrol element position, means responsive to variations inthe magnitudeof a variable for establishing a voltage signal representative of themagnitude of the variable, an automatic controller comprising anoperational amplifier having a passive input impedance and a passivefeedback impedance responsive to said variable representative voltagesignal, said controller bein7 operative to establish an automaticcontrol voltage signal having a predetermined functional relationshipwith said variable representative voltage signal, transfer switch meanshaving a first position for connecting said automatic controller to saidpositioning means to effect automatic positioning of said controlelement in accordance with said automatic control signal and a secondposition for disconnecting said controller from said positioning means,a circuit established by said transfer switch means in said firstposition thereof for rendering said manually operative switch meansinoperative, a circuit established in said second position of saidtransfer switch means for rendering said manually operative switch meansoperative, an electric capacitor, a circuit established in said secondposition of said transfer switch means effective to charge saidcapacitor in proportion to the voltage difference of the outputs of saidautomatic controller and said control element position responsive means,and a circuit established by said transfer switch means in said rstposition thereof effective to connect said capacitor so charged in thecircuit of said controller to thereby equalize the output of saidcontroller with the output of said position responsive means uponactuation of said transfer switch means from said second to said firstposition.

15. In a control system as claimed in claim 14 wherein said controllercomprises a proportional action controller, said input and feedbackimpedances comprising resistances which form a summing junction at theinput to said arnplifier, the last said circuit connecting said chargedcapacitor in series with a resistance between said summing junction andground.

16. In a control system as claimed in claim 14 wherein said controllercomprises a proportional plus integral controller, said input impedancecomprising a resistance and said feedback impedance comprising aresistance connected in series with said capacitor in said firstposition of said transfer switch means, said charging circuitdisconnecting said capacitor from said feedback circuit in said secondposition of said transfer switch means.

17. In a control system, the combination comprising, a final controlelement, positioning means for said control element responsive to anelectrical control signal, means responsive to variations in themagnitude of a variable for 15 establishing an electric signalrepresentative of the variable, an automatic controller havingproportional plus integral action for producing an automatic controlvoltage signal, said controller comprising an operational amplier havinga passive input resistance and a passive feedback circuit including anelectric capacitor for introducing said integral action, a manuallyadjustable controller for establishing a manual control voltage signal,switch means having a first position for connecting said automaticcontroller to said positioning means to effect automatic positioning ofsaid control element in accordance with said automatic control signaland a second position for connecting said manual controller to saidpositioning means to eflect manual positioning of said control elementin accordance with said manual control sig nal, and a circuitestablished by said switch means in said second position thereofeffective to disconnect said capacitor from said feedback circuit toterminate integrating operation of said automatic controller duringcontrol of said control element from said manually adjustablecontroller.

18. In a process control system, the combination comprising, a finalcontrol element, operating means for said control element, meansresponsive to variations in the magnitude of a process variable forestablishing an electric signal representative of the variable, anautomatic controller responsive to said variable representative signalfor establishing an automatic control signal having a predeterminedfunctional relationship to said variable representative signal, anadjustable controller for establishing a second variable control signal,transfer switch means for selectively connecting one of said controllersto said operating means, and means associated with each of said controlers responsive to the difference in magnitude of said second andautomatic control signals for equalizing the output of its associatedcontroller with the output of the other controller during transfer ofcontrol of said control element from said other controller to its saidassociated controller.

19. In a process control system, the combination comprising, a finalcontrol ele-ment, means responsive to an electric control signal foroperating said control element, an automatic controller for producing anoutput control signal representative of the magnitude of a variable,said controller comprising an operational amplifier having an externalpassive impedance element for introducing a predetermined controlcharacteristic into said automatic control signal, a manually adjustablecontroller having a manually adjustable output control signal, transferswitch means having a first position for connecting said automaticcontroller to said positioning means and a second position forconnecting said manual controller to said positioning means, meansincluding said impedance element responsive to the difference inmagnitude of said automatic and manual control signals in said secondposition of said switch means for equalizing said automatic and manualcontrol signals during transfer from manual to automatic control, andmeans responsive to the difference in magnitude of said automatic andmanual control signals in said first position of said switch means forequalizing said automatic and manual control signals during transferfrom automatic to manual control.

References Cited in the file of this patent UNITED STATES PATENTS2,734,155 Schuck Feb. 7, 1956 UNITED STATES PATENT oEEICE CERTIFICATE OFCORRECTION Patent No. 3,068,387 December 1l, 1962 Harold H Koppel lt ishereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 5, line 7l, for "Conecte". read Contacts column lO, lines 34 and35, for the left-hand portion of zo" z i', equation 16, for ec2 em eread eC2 em e3 line'si152 `and 53, the left-hand portion of equation 19,for read ee4 column 13, line 55, for the claim reference numeral "18"read 1l u; column 14, line 24, after "element" insert a comma Signed andsealed this 3rd day of September 1963,l

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER AttrestingOfficer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo., 3,063,387 December 11, 1962 Harold It, Koppel It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 5, line 71, for "Conacts" read Contacts column 10, lines 34 and35, for the left-hand portion of l' H -f equation 16, for eC2 em e readeC2 em e3 1i'nes52 `and 53, the left-hand portion of equation 19, forread e4L column 13, line 55, for the claim reference numeral "18" read1l column 14, line 24, after "element insert a comma.a

Signed and sealed this 3rd day of September 1963o (SEAL) Attest:

DAVID IJ. LADD ERNEST W. SWIDER Commissioner of Patents AttestingOfficer

